Because no one envisioned sound as a business necessity, the only provision early PCs made for sound was a $0.29 speaker driven by a square-wave generator to produce beeps, boops, and clicks sufficient for prompts and warnings. Reproducing speech or music was out of the question. Doing that required an add-on sound card, and those were quick to arrive on the market as people began playing games on their PCs. The early AdLib and Creative Sound Blaster sound cards were primitive, expensive, difficult to install and configure, and poorly supported by the OS and applications. By the early 1990s, however, sound cards had become mainstream items that shipped with most PCs. By 2001 most motherboards included at least basic embedded audio, and by 2003 it was difficult to find a mainstream system or motherboard without good built-in audio.
Properly, the term sound card applies to expansion cards, while sound adapter or audio adapter applies to any component used to provide PC audio, whether as an expansion card or as a device embedded on the motherboard. But like most people, we use these terms interchangeably.
With a sound adapter and appropriate software, a PC can perform various tasks, including:
Playing audio CDs, either directly or from compressed digital copies of the CD soundtracks stored as MP3 or Ogg Vorbis files on your hard disk
Playing stereo music, sound effects, and/or voice prompts in games, education, training, and presentation software, as well ...